1. Field of the Invention
The present invention relates to temperature control apparatuses for controlling the temperature of a heating unit.
2. Description of the Related Art
In a xerographic apparatus such as a copy machine, a toner image formed on a photo-sensitive drum is transferred to a sheet of transfer paper by a transfer device. The toner image on the transfer paper is thermally fused to the transfer paper by a heat fuser. A fusing roller incorporated in the heat fuser includes a built-in heater for heating the fusing roller so that the temperature of the surface of the fusing roller is maintained at a constant temperature.
A temperature control apparatus for such a fuser includes, for example, the temperature control apparatuses shown in FIG. 11 or FIG. 13.
The temperature control apparatus shown in FIG. 11 will now be described. An AC power supply 103 is connected through a switching circuit 104 to a heater 102 of a fusing roller 101. A thermistor 105 converts the temperature of the surface of the fusing roller 101 into an output signal a which has a voltage value in accordance with the temperature. The output signal a is input to an input port P0 of a microcomputer 106 and is subjected to A/D conversion. When a detected temperature is lower than a target temperature, the microcomputer 106 outputs H (ON) from an output port P1 to the switching circuit 104 (signal b). When the detected temperature is higher than the target temperature, the microcomputer 106 outputs L (OFF) from the output port P1 to the switching circuit 104.
A thermoswitch 107 is connected between the AC power supply 103 and the heater 102. When the microcomputer 106 continuously turns ON the output port P1 that controls ON/OFF of the switching circuit 104 as a result of the microcomputer 106 being out of control due to electric noise, a software bug, etc, the switching circuit 104 is continuously ON. As a result, the temperature of the fusing roller 101 increases excessively. In response to that condition, the thermoswitch 107 is operated so as to cut off the power supply to the fusing roller 101.
The temperature control apparatus shown in FIG. 12 will now be described. The AC power supply 103 is connected through the switching circuit 104 to the heater 102 of the fusing roller 101. The thermistor 105 converts the temperature of the surface of the fusing roller 101 into the output signal a including the voltage value in accordance with the temperature. The output signal a is input to an input port P0 of a microcomputer 116 and is subjected to A/D conversion. Bit 3 of a register 1167 that controls the output port P1 of the microcomputer 116 is assigned to switch ON/OFF the heater 102. When a detected temperature obtained by converting the signal a input to the input port P0 into a temperature is lower than a target temperature, the microcomputer 116 writes, for example, 1, instructing xe2x80x9cheater-ONxe2x80x9d to bit 3 of the register 1167. Accordingly, H (ON) is output from the output port P1 to the switching circuit 104 (signal b). In contrast, when the detected temperature is higher than the target temperature, the microcomputer 116 writes 0 instructing xe2x80x9cheater-OFFxe2x80x9d to bit 3 of the register 1167. Accordingly, L (OFF) is output from the port P1 (signal b). Bits other than bit 3 of the register 1167 are assigned to control other input/output ports. The thermoswitch 107, which cuts off the power supply to the heater 102 in case of excessive temperature rise of the fusing roller 101, is connected between the AC power supply 103 and the heater 102.
The temperature control apparatus shown in FIG. 13 will now be described. Unlike the temperature control apparatus shown in FIG. 12, a register 1207 for writing 1 and 0 instructing heater ON/OFF is provided in an integrated circuit (IC) 120 outside a microcomputer 126. An address bus, a data bus, and a control signal of the microcomputer 126 are connected to the IC 120.
In the temperature control apparatuses shown in FIGS. 11 to 13, the thermoswitch 107, which is supposed to operate in case of excess temperature rise, may not operate immediately when the temperature of the fusing roller 101 excessively increases. For example, when the temperature of the fusing roller 101 excessively increases from room temperature, the fusing roller 101 and a bus of the fusing roller 101 may break before the thermoswitch 107 is operated since it takes time before the temperature of the thermoswitch 107 increases.
In order to solve this problem, for example, a method is described in Japanese Laid-Open Patent No. 4-136881. According to the method, electricity to a heater is forced to be periodically turned OFF for a predetermined period of time. When a heater ON/OFF detection unit detects that the heater has been in the ON state for a predetermined period of time or longer, electricity to the heater is cut off.
According to the method, when electricity to the heater is cut off in response to a failure detected, it is impossible to determine whether the failure has occurred in a switching circuit such as a solid-state relay (SSR) or in a microprocessor.
Even when the temperature of a fusing roller is low, the power supply to the heater is periodically turned ON/OFF. As a result, the AC power supply voltage varies in accordance with interruption of current flowing to the heater during power feeding and cut-off periods.
In the temperature control apparatus shown in FIG. 12, the heater 102 is turned ON by simply writing 1 to bit 3 of the register 1167. A failure due to a simple bug in the program of the microcomputer 116 or noise may turn ON the heater 102.
In particular, because bits other than bit 3 of the register 1167 are assigned to other input/output ports, the register 1167 is frequently accessed for purposes other than turning ON/OFF the heater 102. Accordingly, bit inversion may occur as a result of electric noise generated when the register 1167 is accessed for purposes other than heater ON/OFF, thus unnecessarily turning ON the heater 102.
In the temperature control apparatus shown in FIG. 13, the IC 120 is provided outside the microcomputer 126; the address bus, the data bus, and the control signal of the microcomputer 126 are connected to the IC 120; and the microcomputer 126 writes to the register 1207 in the IC 120. When controlling ON/OFF of the heater 102, the buses and control signal may be influenced by electric noise.
When the microcomputer 126 tries to gain write access to another address, part of the address may be inverted by electric noise. The IC 120 may erroneously detect this as writing to the register 1207.
In response to the false detection, the heater 102 may be turned ON. When the register 1207 is accessed to rewrite bits assigned to other functions, bit 3 for heater ON/OFF may be inverted by electric noise. As a result, the heater 102 may be turned ON unnecessarily.
Accordingly, it is a first object of the present invention to provide a temperature control apparatus for solving the foregoing problems and for stopping the power supply to a heater before the temperature of a fusing roller excessively increases.
A second object of the present invention is to provide a temperature control apparatus for solving the foregoing problems and for detecting a failure in the temperature control apparatus without unnecessarily turning ON/OFF a heater even when it is necessary to continuously supply electricity to the heater.
A third of object of the present invention is to provide a temperature control apparatus for solving the foregoing problems and for preventing a malfunction due to electric noise.
In accordance with these and other objects, there is provided a temperature control apparatus that includes a temperature detector for detecting the temperature of a heating unit; a switching circuit for turning ON/OFF the power supply to the heating unit in accordance with an ON/OFF instruction; and an instruction unit for instructing, every predetermined period of time, the switching circuit to turn ON the power supply when the temperature detected by the temperature detector is lower than a target temperature and to turn OFF the power supply when the detected temperature is higher than the target temperature. A determination unit determines that a failure has occurred when no instruction is given from the instruction unit within a preset time longer than the predetermined period of time. When the determination unit determines that the failure has occurred, the power supply to the heating unit is turned OFF.
In another aspect, the determination unit includes a generation unit for generating a failure detection signal when it is determined that the failure has occurred; and a latch unit for latching the failure detection signal generated by the generation unit. The switching circuit may turn OFF the power supply to the heating unit while the failure detection signal is being latched by the latch unit.
The temperature control apparatus may also include an initialization unit for initializing the temperature control apparatus when the determination unit determines that the failure has occurred.
The initialization unit initializes the temperature control apparatus except for the latch unit. A failure-signal maintaining unit may be provided to prevent the power to be again supplied to the heating unit after the initialization.
The determination unit includes an informing unit for reporting the occurrence of the failure when it is determined that the failure has occurred.
In accordance with one aspect of the present invention, the heating unit may include a fusing roller with a heater, or an induction coil and an electromagnetic-induction heating member, and the temperature detector may include a contact-type temperature sensor, such as a thermistor, for making contact with an object and detecting the temperature of the object, or a non-contact-type temperature sensor, such as a built-in thermistor, for detecting the temperature of an object without making contact with the object.
According to another aspect of the present invention, a temperature control apparatus includes a temperature detector for detecting the temperature of a heating unit; a switching circuit for turning ON/OFF the power supply to the heating unit in accordance with an ON/OFF instruction; an instruction unit for instructing, every predetermined period of time, the switching circuit to turn ON the power supply when the temperature detected by the temperature detector is lower than a target temperature and to switch OFF the power supply when the detected temperature is higher than the target temperature. The instruction unit instructs the switching circuit to turn OFF the power supply at least once in each predetermined period of time. A determination unit determines that a failure has occurred when the OFF-instruction is not given from the instruction unit within a preset time which is longer than the predetermined period of time. When the determination unit determines that the failure has occurred, the power supply to the heating unit is turned OFF.
In accordance with yet another aspect of the invention, the determination unit includes a generation unit for generating a failure detection signal when it is determined that the failure has occurred; and a latch unit for latching the failure detection signal generated by the generation unit. The switching circuit may turn OFF the power supply to the heating unit while the failure detection signal is being latched by the latch unit.
The temperature control apparatus may also include an initialization unit for initializing the temperature control apparatus when the determination unit determines that the failure has occurred. The initialization unit initializes the temperature control apparatus except for the latch unit. The switching circuit may turn OFF the power supply to the heating unit while the failure detection signal is being latched by the latch unit after the initialization of the temperature control apparatus except for the latch unit.
In accordance with still another aspect of the invention, the temperature control apparatus further includes an informing unit for reporting the occurrence of the failure when the determination unit determines that the failure has occurred.
In accordance with yet another aspect of the invention, the heating unit may include a fusing roller with a heater, or an induction coil and an electromagnetic-induction heating member.
According to another aspect of the present invention, a temperature control apparatus includes a temperature detector for detecting the temperature of a heating unit; an instruction unit for giving an ON-instruction when the temperature detected by the temperature detector is lower than a target temperature and to give an OFF-instruction when the detected temperature is higher than the target temperature; first to n-th (xe2x89xa72) registers; a first setting unit for setting a first predetermined value to the first register when the ON-instruction is given by the instruction unit and to set a second predetermined value when the OFF-instruction is given by the instruction unit; a second setting unit for setting, before the first setting unit sets the first predetermined value to the first register, third to (n+1)-th predetermined values to the second to the n-th registers every time the ON-instruction is given by the instruction unit; a determination unit for determining whether or not the contents of the second to the n-th registers match the third to the (n+1)-th predetermined values, respectively, and to determine that the temperature control apparatus is in a heating-unit-ON-permitted state when the contents match the predetermined values; and a switching circuit for turning ON the power supply to the heating unit when it is determined by the determination unit that the temperature control apparatus is in the heating-unit-ON-permitted state and when the first predetermined value is set to the first register, and, when the first setting unit sets the second predetermined value to the first register, to turn OFF the power supply to the heating unit. Preferably, the second to the n-th registers each include an address differing from that of the first register.
In accordance with still another aspect of the invention, the temperature control apparatus further includes a clearing unit for clearing the second to the n-th registers when the determination unit determines that the temperature control apparatus is in the heating-unit-ON-permitted state and when the first predetermined value is set to the first register.
The temperature control apparatus further includes a clearing unit for clearing the first register when the determination unit determines that the temperature control apparatus is in the heating-unit-ON-permitted state and when the first predetermined value is set to the first register.
Preferably, the second to the n-th registers are cleared when the second predetermined value is set to the first register, and when not in the case that the contents of the second to the n-th registers are cleared values, or the third to the (n+1)-th predetermined values, respectively, it is determined that a failure has occurred and the switching circuit turns OFF the power supply to the heating unit. When not in the case that the content of the first register is a cleared value, the first predetermined value, or the second predetermined value, it is determined that a failure has occurred and the power supply to the heating unit is turned off.
When the first predetermined value is written to the first register and the temperature control apparatus is not in the heating-unit-ON-permitted state, it is determined that a failure has occurred and the power supply to the heating unit is turned off.
In accordance with still another aspect of the invention, the temperature control apparatus further includes an informing unit for reporting the occurrence of the failure when it is determined that a failure has occurred.
In accordance with still yet another aspect of the invention, the temperature control apparatus further includes an initialization unit for initializing the temperature control apparatus when it is determined that the failure has occurred; a maintaining unit for maintaining the failure state when it is determined that the failure has occurred; and an inhibiting unit for inhibiting the power supply to the heating unit after the initialization by the initialization unit when the failure state is maintained by the maintaining unit.
According to another aspect of the present invention, a temperature control apparatus includes a temperature detector for detecting the temperature of a heating unit; an instruction unit for giving an ON-instruction when the temperature detected by the temperature detector is lower than a target temperature and to give an OFF-instruction when the detected temperature is higher than the target temperature; first to m-th (xe2x89xa73) registers; a first setting unit for setting a first predetermined value to the first register when the ON-instruction is given by the instruction unit; a second setting unit for setting a second predetermined value to the second register when the OFF-instruction is given by the instruction unit; a third setting unit for setting third to m-th predetermined values to the third to the m-th registers, respectively, before the first setting unit sets the predetermined value to the first register; a determination unit for determining whether or not all the contents of the third to the m-th registers match the third to the m-th predetermined values, respectively, and to determine that the temperature control apparatus is in a heating-unit-ON-permitted state when the contents match the predetermined values; and an ON/OFF for turning ON the power supply to the heating unit when the determination unit determines that the temperature control apparatus is in the heating-unit-ON-permitted state and when the first predetermined value is set to the first register and, when the second predetermined value is set to the second register, to turn OFF the power supply to the heating unit.
Preferably, the first to the m-th registers each include an address differing from that of a register other than the first to the m-th registers, or the first to the m-th registers include different addresses.
The temperature control apparatus may further include a clearing unit for clearing the first register and the third to the m-th registers when the determination unit determines that the temperature control apparatus is in the heating-unit-ON-permitted state and when the first predetermined value is set to the first register.
When the contents of the third to the m-th registers are cleared or differ from the third to the m-th predetermined values, respectively, it is determined that a failure has occurred and the power supply to the heating unit is turned off.
When not in the case that the content of the first register is a cleared value or the first predetermined value, it is determined that a failure has occurred and the power supply to the heating unit is turned off.
When the first predetermined value is written to the first register and the temperature control apparatus is not in the heating-unit-ON-permitted state, it is determined that a failure has occurred and the power supply to the heating unit is turned off.
The temperature control apparatus may further include an informing unit for reporting the occurrence of the failure when it is determined that the failure has occurred; an initialization unit for initializing the temperature control apparatus when it is determined that the failure has occurred; a maintaining unit for maintaining the failure state when it is determined that the failure has occurred; and an inhibiting unit for inhibiting the power supply to the heating unit after the initialization by the initialization unit when the failure state is maintained by the maintaining unit,
According to the present invention arranged as described above, the power supply to the heater can be stopped before the temperature of the fusing roller excessively increases.
According to the present invention arranged as described above, when it is necessary to have the heater continuously turned ON, a failure in the temperature control apparatus can be detected without unnecessarily turning ON/OFF the heater. According to the present invention, a malfunction due to electric noise can be prevented.
Further objects, features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.